Hydrostatic transmission connection apparatus

ABSTRACT

A transaxle assembly having at least two transaxle housings for a zero turn or similar vehicle, where both housings mount separate hydrostatic transmissions. A mounting plate is provided to secure to both of the housings to mount the housings to a vehicle frame and if required to seal openings formed in the bottom of both of the housings. The connection plate may include tabs or other structure to secure it to the vehicle frame to increase the ease of assembly of the transaxle unit in the vehicle.

RELATED APPLICATION

This application claims the benefit of and is a continuation of U.S.application Ser. No. 10/634,356 filed Aug. 5, 2003, now U.S. Pat. No.6,817,430 which is a continuation of patent application Ser. No.10/056,570 filed on Jan. 25, 2002, now U.S. Pat. No. 6,644,425, both ofwhich are incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

This invention relates to an apparatus used to connect hydrostatictransaxles and, more particularly, a plate or similar structure used toconnect a pair of hydrostatic zero turn transaxles for use on a lawn andgarden tractor or similar vehicle. Hydrostatic transaxles are known inthe art and generally comprise a hydrostatic transmission mounted in ahousing with reduction gearing, one or more output axles and otherelements. The term transaxle is used broadly to cover both integratedunits, where the hydrostatic transmission is in a common housing and oilsump with the gearing elements, and other designs where the transmissionmay be formed in a separate housing and oil sump.

Zero turn transaxles are also well-known in the art. One well-knowndesign is the Agri-Fab Model 2500 transmission. One embodiment of thisdesign is shown in U.S. Pat. No. 5,078,222. This 2500 transaxlegenerally uses a pair of hydrostatic transmissions, each of which drivesa gear reduction to separately power the two vehicle axles. Thisarrangement permits the vehicle operator to separately drive the twodrive wheels independently of one another. Another known zero turndesign in the Eaton Model 751, which uses a pump and motor mounted atright angles to one another, with the hydraulic pump, motor and axlemounted in a housing. Obviously, a vehicle requires a pair of such zeroturn units mounted side by side to drive the two drive wheels, and thegeneral shape and configuration of the transaxle housing is dictatedprimarily by the size and shape of the vehicle frame, and similarfactors.

Zero turn transaxles are generally manufactured separately from thevehicles and sold to a vehicle manufacturer for incorporation into thevehicle, such as a lawn mower or similar product. The vehiclemanufacturer will generally create custom mounting arrangements to mountthe zero turn transaxles separately on the vehicle frame. Each custommounting arrangement requires costly tooling and can increase thedifficulty of assembly for the vehicle manufacturer.

In addition, when two units are mounted side by side and secured to thevehicle frame at the top of the transaxle housing, there is inherentlycertain torque applied to the units, causing the units to flex withrespect to one another, which leads to unnecessary stress and wear onvarious components. In such designs it has been known to provide anadditional member to connect the two units together to prevent suchflexing. This additional member also increases the cost of the unit.

SUMMARY OF THE INVENTION

It is an object of the invention to eliminate such problems by providinga single plate device on which both zero turn transaxles can be mounted.Such hydrostatic transaxles may have at least one cap plate on thebottom of the transaxle housing. In one embodiment, the connection plateitself forms an integral part of the two transaxle housings to close offa portion thereof, thereby eliminating the need for an additional cappiece and reducing the overall cost and weight of the unit. In a furtherembodiment of the invention this plate is secured to two separate andcomplete transaxle housings.

In a preferred embodiment of this invention, the connection plate isformed of stamped steel, which would have sufficient strength to act asa skid plate for the transaxle assembly, thus eliminating the need forsuch an additional piece.

A further benefit of this invention is that the two transaxle units canbe assembled together with the connection plate, thus simplifying laterassembly of the unit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a back portion of a vehicle incorporating aprior art design of a zero turn transaxle assembly.

FIG. 2 is a an exploded perspective view of a simplified version ofanother prior art zero turn transaxle design.

FIG. 3 is a front view of a portion of a vehicle frame and a zero turnassembly in accordance with the present invention.

FIG. 4 is a perspective view of one embodiment of a connection plate ofthe present invention.

FIG. 5 is a perspective view of a second embodiment of a connectionplate of the present invention.

FIG. 6 is an end view of a third embodiment of a connection plate inaccordance with this invention.

FIG. 7 is a plan view of the connection plate shown in FIG. 6.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a prior art design of a vehicle having a pair of zero turntransaxles 14 a and 14 b including housings 16 a and 16 b, respectively,secured to a vehicle frame 18 through a plurality of bolts 19 or similarfastening means on housings 16 a and 16 b. Transmissions 14 a and 14 beach drive an axle 20 a and 20 b which are secured to wheels and tires22 a and 22 b respectively. In the design shown in FIG. 1, each of thecap plates 15 a and 15 b are secured to the bottom of the housings 16 aand 16 b through a plurality of bolts 17 or similar fasteners. Theopenings in the housings 16 a and 16 b are generally used for assemblyof the hydrostatic units; such openings are not required, nor is itrequired that such openings be formed at the bottom of the transaxlehousing, as other housing designs could be used. For example, it is alsoknown to form transaxle or transaxle casings of two main casing portionsjoined together along a split line.

FIG. 2 shows another prior art arrangement, showing transaxle housings16 a and 16 b in a simplified view of a typical application to moreclearly show the connection to the vehicle frame and related elements,including transaxle mounting plate 12, engine cowling 13 and front framemember 21. In this prior art design, tabs 27 are formed on both sides ofeach housing 16 a and 16 b to permit them to be bolted or otherwisesecured to mounting plate 12. Only the inboard tab 27 is shown onhousing 16 b and the outboard tab 27 is shown on housing 16 a; it willbe understood that matching tabs are present on the other side of eachhousing. Plate 12 may also be secured to housings 16 a and 16 b at thefront portions thereof. As can be seen, both of the housings 16 a and 16b will need to be separately bolted to mounting plate 12 duringassembly; frame elements 12, 13 and 21 are all secured together in theembodiment shown.

However, this design does not provide sufficient rigidity to preventflexing of the two transaxle units 14 a and 14 b with respect to eachother. For example, there is insufficient rigidity to prevent rotationof axle 20 a about an axis parallel to the length of the transaxlehousings 16 a and 16 b and located approximately at the outboard tabs27. As the vehicle traverses uneven ground the axles will tend to flexabout these axes, putting stress on mounting locations and otherportions of the vehicle, risking fatigue and loosening of fasteners.Thus, even though housings 16 a and 16 b are attached to plate 12 in atleast four locations, there is insufficient rigidity to prevent flexingof mounting plate 12. One known solution is to create a boss on thebottom of both of the transaxle housings 16 a and 16 b and have a rodconnecting one housing to the other; however, this causes additionalexpense and difficulty in assembly.

FIG. 3 shows a zero turn transaxle assembly in accordance with oneembodiment of the present invention. As in the prior art, transaxles 14a and 14 b each include housings 16 a and 16 b, respectively, which aresecured to rails of vehicle frame 18 at the top portion thereof throughbolts 19. This discussion will focus on transaxle 14 a; it will beunderstood that these comments will apply equally to the correspondingtransaxle 14 b. Transaxle housing 16 a includes a hydrostatic pump (notshown) which is driven by pump input shaft 23 a by means of pulley 26 a.The details of the inner workings of the hydrostatic transaxle are notimportant to the invention and it will be understood that this inventioncould also be applied to other designs. It will be understood that thehydraulic pump and motor operate together to drive output axle 20 a. Acontrol arm (not shown) is used to control the output and direction ofthe hydrostatic transaxle and in one known design, the control arm wouldcontrol a swash plate to control the hydraulic output of the pump. Otherknown control methods could be used. Cooling fan 24 a is also driven bypulley 26 a to provide cooling for the unit.

As shown in FIGS. 3 and 4, plate 30 is secured to both of the housings16 a and 16 b through a plurality of bolts 32 or similar fastenersmounted through mounting holes 35 which can be formed at various placeson the plate. Plate 30 acts to seal openings in the respective transaxlehousings, thus replacing the separate cap plate used in prior artdesigns. The necessary seals can be used to prevent the leakage ofhydraulic fluid. It is preferred to use a liquid sealant/adhesive tocreate this seal, but a formed or cut gasket would also suffice. Plate30 may also include a front tab 37 and rear tab 39 to increase therigidity of the plate by adding a strengthening rib between thetransaxles, to reduce flexing between transaxles 14 a and 14 b. Tabs 37and 39 optionally can include a plurality of mounting slots 40 forsecuring the plate 30 to vehicle frame 18; these slots permit a widerange of mounting possibilities to permit use with differentmanufacturers' designs. This permits the use of a single plate designwith multiple transaxle or vehicle frame designs, eliminating the needto custom-design these plates.

FIG. 5 shows an alternative embodiment of plate 30, where front tab 38is enlarged to act as a debris shield to protect the transaxles fromdebris that may be kicked up by the vehicle or from other sources.Additional debris shields could be formed at other places, such as alongthe sides of the plate, depending on the intended application. Tab 38also includes a plurality of linkage openings 42 which can be formed atany place along tab 38 as may be required by the shape and size of thetransaxle, the vehicle linkages, location of the belts and the like.These openings would preferably be stamped, but other methods could beused. Tab 38 also includes a plurality of vent openings 43 to allow airflow to the transaxle for cooling purposes. The size of these openingswould depend on the amount of air flow needed and similar designchoices. FIG. 5 also shows that mounting openings 41 can be used inplace of slots 40. It will also be understood that the plate could beformed as a solid piece without the various openings other than mountingholes; in such an embodiment it would be preferred to punch smalldrainage holes in the plate to remove any water that may accumulatethere.

FIGS. 6 and 7 show a further embodiment of the invention where plate 31is not formed to create a cap plate to seal the transaxle housings, butrather is used solely to secure the two housings together. In thisembodiment, plate 31 includes a plurality of openings 45 in front tab 44to secure plate 31 to a vehicle frame. This plate need not be directlysecured to the vehicle frame but could also be used simply as a means ofstrengthening the connection between the two transaxle units. Mountingslots 46 are stamped in the main surface of plate 31 in a variety oflocations to provide maximum flexibility for securing it to thetransaxle housings in different locations to accommodate different framewidths. The function of mounting slots 46 could also be performed byother features such as multiple holes, welded thread studs or similarfeatures, which could also be used to provide multiple mountinglocations. The embodiment shown in FIGS. 6 and 7 does not contemplatethe use of the plate to close any openings in the transaxle housings,but rather acts to secure the units together in a unitary mountingpackage.

It will be understood that the above description should not be read aslimiting the scope of this invention, as further features and benefitswill be obvious to one skilled in the art. This invention should be readas limited by the claims only.

1. A transaxle assembly comprising: a first transaxle housing having afirst sump formed therein, and a first opening formed in the firsttransaxle housing; a second transaxle housing having a second sumpformed therein, and a second opening formed in the second transaxlehousing; and a connection member secured to both the first and secondtransaxle housings, wherein the connection member closes the firstopening to seal the first sump and closes the second opening to seal thesecond sump.
 2. The transaxle assembly of claim 1, wherein theconnection member comprises a plate.
 3. The transaxle assembly of claim1, further comprising a first hydrostatic transmission mounted in thefirst sump and a second hydrostatic transmission mounted in the secondsump.
 4. The transaxle assembly of claim 2, wherein the plate furthercomprises at least one tab extending generally perpendicular to theplate.
 5. The transaxle assembly of claim 4, wherein the tab comprisesat least one opening.
 6. The transaxle assembly of claim 4, wherein thetab comprises at least one slot.
 7. The transaxle assembly of claim 1,wherein the connection member further comprises an attachment to avehicle frame.
 8. The transaxle assembly of claim 1, wherein the firsttransaxle and the second transaxle each comprise generally collinearaxle shafts extending away from each other.
 9. A vehicle comprising: afirst transaxle comprising a first housing forming a first sump; asecond transaxle comprising a second housing forming a second sump; avehicle frame to which the first and second transaxle housings areattached, the bottom surface of the vehicle frame generally establishinga first plane; and a plate member attached to the first and secondtransaxle housings, the plate member establishing a second planegenerally parallel to the first plane and substantially separated fromthe first plane.
 10. The vehicle of claim 9, wherein the plate member isattached to the vehicle frame by a connection member.
 11. The vehicle ofclaim 10, wherein the connection member between the plate member and thevehicle frame is generally perpendicular to the first and second planes.12. The vehicle of claim 11, wherein the connection member is integrallyformed as part of the plate member.
 13. The vehicle of claim 9, whereinthe first transaxle and the second transaxle comprise hydrostatictransmissions.
 14. The vehicle of claim 9, wherein the plate member hasa plurality of mounting positions in which to attach the first andsecond transaxle housings.
 15. The vehicle of claim 14, wherein theplurality of mounting positions is generally parallel to axle shaftsextending from the first and second transaxles.